1. Field of the Invention
The present invention relates to a combustion chamber of an internal combustion engine.
2. Description of the Related Art
Known in the art is an internal combustion engine wherein a pair of exhaust valves are arranged on one side of an inner wall of a cylinder head, three intake valves are arranged on the other side of the inner wall of the cylinder head, and the air-fuel mixture is made to flow to the combustion chamber from only the valve openings of the intake valves formed on the exhaust valve side by covering the valve openings of the intake valves formed on the opposite side from the exhaust valves by masking walls to thereby cause the generation of a swirl flow about a horizontal axis, that is, a tumble flow, inside the combustion chamber (see Japanese Unexamined Patent Publication (Kokai) No. 4-159419).
If a tumble flow is made to be generated in the combustion chamber as in the above-mentioned internal combustion engine, the combustion rate is made faster and thus good combustion can be obtained. However, in this internal combustion engine, since the valve openings of the intake valves are covered by the masking walls over a wide range, there is a problem in that the filling efficiency is lowered at the time of a high load operation of the engine and thus a high engine output cannot be obtained. Namely, the most important thing when causing the generation of such a tumble flow is how to cause the generation of a strong tumble flow while preventing the reduction of the filling efficiency.
The first method which is thought of as a method of improving the filling efficiency in such an internal combustion engine is to enlarge the valve diameter of the intake valves so as to enlarge the opening part of the intake valves not covered by the masking walls. However, there is a limit to the enlargement of the valve diameter of the intake valves--the filling efficiency cannot be sufficiently enhanced just by enlarging the valve diameter of the intake valves. However, the inventors engaged in experiments and studies and as a result discovered that the strength of the tumble flow was governed by the tumble flow generated at a center portion of the combustion chamber and accordingly if a masking wall is formed focused to cause generation of a tumble flow at the center portion of the combustion chamber, a sufficiently strong tumble flow could be generated.
When this fact is known, it becomes sufficient to consider only causing generation of a tumble flow at the center portion of the combustion chamber, so it becomes possible to reduce the dimensions of the masking walls in comparison with the case of causing generation of a tumble flow in the entire combustion chamber and thus it becomes possible to improve the filling efficiency. In this case, the smaller the dimensions of the masking walls are made, the more improved the filling efficiency becomes, so the focus becomes at which position the masking walls should be formed for generating the strongest tumble flow even by masking walls with the smallest dimensions.
On the other hand, even if the dimensions of the masking walls can be made smaller in this way, in so far as the masking walls is provided, the filling efficiency is lowered by only the amount of coverage by the masking walls. Accordingly, even if the dimensions of the masking walls can be made smaller in this way, consideration must be given to further improvement of the filling efficiency.